THE INFLUENCE OF CHROMIUM ADDITION ON THE TOUGHNESS OF GAMMA-NI ALPHA-AL2O3 INTERFACES/

Experimental studies designed to characterize the fracture resistance of interfaces between Al2O3 and either pure Ni or a gamma-Ni alloy con taining Cr have revealed a profound influence of Cr on the debond toug hness. The interface between the pure Ni and Al2O3 is susceptible to s tress corrosion caused by moisture, resulting in a fracture energy of the order of 10 J/m(2). The interface between the alloy and the Al2O3 cannot be fractured, even at strain energy release rates in excess of 100 J/m(2). An analysis of these interfaces has identified two influen ces of the alloy addition that might govern its role in eliminating st ress corrosion: (i) the Cr ''getters'' the C near the interface by for ming a Cr-carbide reaction product, and (ii) the alloy dissolves some of the alumina during bonding, exposing virgin material to the alloy a t the interface. The factors that lead to carbide formation and alumin a dissolution are discussed. (C) 1997 Acta Metallurgica Inc.